<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>钉钉选择文件</title>
</head>
<body>
  <input type="file" multiple onchange="handleChange()"/>

  <script>
    function handleChange (event) { 
      event = event || window.event;
      alert("file len is：" + (event.target.files || []).length);
    }
  </script>
</body>
</html>